The brown, red, orange, and white are related to the radio and other circuits.
Red supplies power to the radio.
Orange is for the light in the radio when you turn the headlights on.
Ignore the white. This is supplying power to another circuit.
That leaves black and green which most likely are the speaker wires. Black for ground, brown for +. Look up under the dash and see what color wires are coming off the in-dash speakers to be sure.
Here is a diagram. Speaker wires are not shown.
http://70duster440.com/DashHarness70 Page 1.PDF
